Engine control systems employ exhaust gas recirculation (EGR) mechanisms to regulate exhaust emissions and improve fuel economy. External EGR is also used by automotive manufacturers to improve fuel economy. EGR improves fuel economy by reducing pumping losses at part throttle (that is, EGR can lower engine pumping work by increasing intake manifold pressure). Further, by adding cooled EGR, the tendency for spontaneous ignition initiated via spark-ignited combustion, may be reduced.
EGR involves recirculating exhaust gas from the exhaust manifold into the intake manifold through a flow control valve placed in the path of the EGR flow in between the exhaust manifold and the intake manifold. In doing so, exhaust gases are added to the air-fuel mixture. EGR amount may be calculated by a controller based on manifold absolute pressure (MAP) of the intake manifold and a differential pressure measured across a fixed orifice located downstream of the flow control valve. Based on the EGR amount, a cylinder air charge is estimated and accordingly, fuel injection may be adjusted to control air/fuel ratio.
One example method for EGR flow and air flow estimation is shown by Russell et al. in U.S. Pat. No. 6,944,530. Therein, the manifold pressure sensor is used to measure the pressure downstream of the orifice and a single absolute pressure sensor is used to measure the pressure upstream of the orifice. Based on the calculated differential pressure across the orifice, EGR flow is estimated and subsequently cylinder air charge may be estimated.
However, the inventors herein have identified potential disadvantages with such approaches. As one example, the above approach utilizes two different sensors to measure MAP and differential pressure across the orifice. Such operation may result in the MAP sensor either being positioned away from a desired measurement location in the intake manifold (resulting in potentially inaccurate MAP readings), or a measurement tube enabling the MAP sensor to be positioned at a remote location (resulting in lagging MAP readings). In one example, inaccuracies in EGR estimation may occur due to a lag between MAP and EGR differential pressure signals. Transient errors in EGR mass estimation can cause errors in estimated air mass which may consequently result in errors in fuel delivery and air-fuel ratio control, precisely when accurate EGR determination is most needed (due to the delay in air-fuel ratio sensor feedback identifying such transient fueling errors).
In one example, the above issues may be addressed, at least in part, by a system comprising: an intake manifold, an EGR passage coupled to the manifold with an EGR valve, a sensor housing coupled directly to the manifold, with absolute and differential pressure sensing elements sharing a connection to the manifold. In some examples, an orifice may be positioned downstream of the EGR valve. In this way, by packaging the differential pressure sensor and manifold absolute pressure sensor in a single unit that utilizes a common pressure chamber within which the intake manifold pressure may be measured, any changes in the MAP will result in a simultaneous change in differential pressure eliminating the lag between MAP and differential pressure signals. Further, by inserting the combination sensor directly into the intake manifold, the stand alone differential pressure sensor may be eliminated along with an additional electrical connector and sensor mounting mechanisms resulting in cost saving.
It should be understood that the summary above is provided to introduce in simplified form a selection of concepts that are further described in the detailed description. It is not meant to identify key or essential features of the claimed subject matter, the scope of which is defined uniquely by the claims that follow the detailed description. Furthermore, the claimed subject matter is not limited to implementations that solve any disadvantages noted above or in any part of this disclosure.